For a complete list of publications, click here.
Wehr, J.D. & Whitton, B.A. 1983. Accumulation of heavy metals by aquatic mosses. 2. Rhynchostegium riparioides. Hydrobiologia 100: 261-284.
Abstract: A study was made of general ecology and metal accumulation in the widespread aquatic moss Rhynchostegium riparioides, (Hedw.) C. Jens. with a view to developing the use of this species as a monitor of heavy metal pollution. In order to establish a data bank for statistical analysis, samples of water and moss were taken within a 6-week period from 105 sites (10-m reaches) in Northern England from streams and rivers of diverse physical and chemical types. Analyses were made of 14 metals (Na, Mg, K, Ca, Cr. Mn, Fe, CO, Ni, Cu. Zn, Cd, Ba, Pb) in both 2-cm tips and whole plants. The same 14 metals were also measured in both total and filtrable water, together with 12 other variables. Samples of tips were easier to prepare for analysis, but had significantly (p < 0.001) lower concentrations of all metals except Na and K. Significant correlations (p < 0.001) between metal in moss and aqueous metal were found for ten metals (Na, K, Mg, Ca, Mn, Cu. Zn, Cd, Ba, Pb). Correlations between metals in moss and in water were in general similar for tips and whole plants, but much higher for tips with Na, Zn and Cd; the relationship was quite similar whether total or filtrable water was considered, with the exception of Ba where the correlation was much higher with the latter. A multiple regression was used to suggest which variables in water and/ or moss may influence accumulation of Co, Ni, Cu. Zn, Cd, Ba and Pb in the moss. For instance, the variables which had a very highly significant effect on Pb in tips were Pb, filtrable reactive phosphate and Zn in the water. A discussion is included of how the data may be used for monitoring purposes.
Wehr, J.D. & Brown, L.M. 1985. Selenium requirement of a bloom-forming planktonic alga from softwater and acidified lakes. Can. J. Fish. Aquat. Sci. 42: 1783-1788.
Abstract: Lakewide odor episodes have been associated with blooms of the planktonic alga Chrysochromulina breviturrita Nicholls (Prymnesiophyceae) in lakes influenced by acidic precipitation. We demonstrate an absolute requirement in this flagellate for selenium (Se) in axenic culture. The alga is capable of utilizing several forms of Se: selenite, selenate, dimethylselenide (DMSe), and selenomethionine. This is believed to be the first demonstration of the utilization of DMSe as a Se source by any organism. As the microflora of aquatic sediments recycle Se as volatile DMSe, this may have significance in its biogeochemistry in acidified waters. Bioassays of lake waters from the Muskoka-Haliburton region of Ontario show that in one lake (Dickie) a simulated Se spike resulted in a significant increase (70%, p < 0.05) in algal growth. Growth in Cinder Lake water, which had supported a population of C. breviturrita, was marginally stimulated (24%, p < 0.05). Distant coal-fired power plants, which have been implicated in the episodic deposition of Se, may account in part for the unpredictable blooms of the alga. Chrysochromulina breviturrita cannot be maintained in culture without this micronutrient, and several Se sources may be important triggering factors for the initiation of blooms.
Wehr, J.D., Le, J., and Campbell, L. 1994. Does microbial biomass affect pelagic ecosystem efficiency? An experimental study. Microbial Ecology 27: 1-17.
Abstract: Bacteria and other microorganisms in the pelagic zone participate in the recycling of organic matter and nutrients within the water column. The microbial loop is thought to enhance ecosystem efficiency through rapid recycling and reduced sinking rates, thus reducing the loss of nutrients contained in organisms remaining within the photic zone. We conducted experiments with lake communities in 5400-liter mesocosms, and measured the flux of materials and nutrients out of the water column. A factorial design manipulated 8 nutrient treatments: 4 phosphorus levels x 2 nitrogen levels. Total sedimentation rates were greatest in high-N mesocosms; within N-surplus communities, 1 M P resulted in 50% increase in total particulate losses. P additions without added N had small effects on nutrient losses from the photic zone; +2 M P tanks received 334 mg P per tank, yet after 14 days lost only 69 mg more particulate-P than did control communities. Nutrient treatments resulted in marked differences in phytoplankton biomass (twofold N effect, fivefold P effect in +N mesocosms only), bacterioplankton densities (twofold N-effect, twofold P effects in --N and +N mesocosms), and the relative importance of autotrophic picoplankton (maximum in high N:P mesocosms). Multiple regression analysis found that of 8 plankton and water chemistry variables, the ratio of autotrophic picoplankton to total phytoplankton (measured as chlorophyll a) explained the largest portion of the total variation in sedimentation loss rates (65% of P-flux, 57% of N-flux, 26% of total flux). In each case, systems with greater relative importance of autotrophic picoplankton had significantly reduced loss rates. In contrast, greater numbers of planktonic bacteria were associated with increased sedimentation rates and lower system efficiency. We suggest that different microbial components may have contrasting effects on the presumed enhanced efficiency provided by the microbial loop.
Wehr, J.D., S.P. Lonergan, & J.H. Thorp. 1997. Concentrations and controls of dissolved organic matter in a constricted-channel region of the Ohio River. Biogeochemistry 38: 41-65.
Abstract: A 12-month study was conducted to measure the concentrations of dissolved organic matter (DOC, TDN, TDP) in four sites within the McAlpine Pool, a 119 km long reach of the Ohio River. In this study we test whether specific geomorphological and biological factors influence variations in dissolved organic matter. Concentrations of DOC in the river averaged 1200 mol / L, and varied by nearly two orders of magnitude seasonally (mean DOC during base flow 620 mol / L). Peak periods for DOC at all sites was during April - May. The site nearest a navigation dam (deeper, lower current velocities) had significantly lower concentrations of TDN and greater C:N ratios than upstream sites. The largest tributary entering this pool (Kentucky River) had no significant effect on levels of DOM in the main river, despite having significantly greater concentrations of TDN and lower levels of DOC during most months of the year. Concentrations of DOC, TDN, and TDP were insignificantly different in littoral and pelagic habitats at all sites studied, suggesting little floodplain influence on DOM. C:N ratios of DOM in the Ohio were significantly different among seasons; C:N exceeded or equaled Redfield in summer and fall (6 to 10), but were below Redfield (1.8 to 3.0) during winter and spring. Regression models suggest that total phytoplankton densities and flow conditions are the two most important factors regulating DOM in the Ohio.
Wehr, J. D., and J. H. Thorp. 1997. Effects of navigation dams, tributaries, and littoral zones on phytoplankton communities in the Ohio River. Can. J. Fish. Aquat. Sci. 54: 378-395.
Abstract: Phytoplankton and water chemistry variables were sampled monthly along a 361 km stretch of the Ohio River. We compared (1) regions from Ohio through Kentucky, (2) sites above, below, and within tributaries, (3) nearshore and channel habitats, and (4) sites away from and near navigation dams. Densities of suspended cells were lowest during colder, high-flow periods (31,000 cells / mL), greatest during warmer, low-flow summer (104,000 cells / mL). Of 134 taxa identified, >60% were diatoms, comprising 6% of cell numbers and 28% of total biovolume. Summer assemblages were dominated by colonial Aphanothece saxicola, Merismopedia punctata, Microcystis aeruginosa, and unicellular Synechococcus species. Diatoms Melosira jurgensii and M. distans were abundant in summer; Cyclotella spp. in spring. Concentrations of DIP ((40 (g/L) and DIN ((1100 (g/L) were high; neither was positively correlated with any phytoplankton variable. Interpool declines in picoplankton correlated with greater copepod nauplii densities. Navigation dams significantly reduced current velocity and densities of benthic forms; DIP levels were significantly greater. Near-dam sites had increased biomass of larger phytoplankton (> 2 (m) in winter, but lower densities during summer. Multiple regression identified temperature (+) and current velocity (-) as the main factors affecting phytoplankton densities in this large river.
Page last updated January 28, 1998 by Charles W. Fox (Fox@murray.fordham.edu)